The present invention relates to an appartus for calcining green coke to produce calcined coke. More particularly, the present invention relates to an improved feeding system for feeding green coke into a coke calcining apparatus.
Processes for calcining green coke to produce calcined coke are well-known. Green coke is a carbonaceous material containing various solid hydrocarbons and is derived from various petroleum hydrocarbon fractions. As is, green coke has essentially no use. However, when green coke is heated at an elevated temperature for a sufficient period of time, the various solid hydrocarbons are either driven off or decomposed to yield a solid material comprising essentially carbon. This material, referred to as calcined coke, finds wide use in the manufacture of various types of electrodes such as those used in carbon arc steel and aluminum-making furnaces.
Green coke is conventionally calcined in an apparatus which includes a calcining kiln where the heating operation occurs. The calcining kiln normally takes the form of an elongated rotating cylinder which is tilted slightly so that green coke introduced in the upper end will slowly move through the kiln to the lower end as the kiln rotates. Natural gas is introduced into the lower end of the kiln where it is burned to provide the heat for effecting the calcination reaction. Calcined coke passes out of the lower end of the rotating kiln while gaseous byproducts pass out of the upper end of the kiln.
Since the gaseous byproducts passing out of a coke-calcining kiln contain entrained particulate matter, the gases are usually passed through a dust-settling chamber where the dust and other particles settle out. Then, the gases pass to the bottom of an off-gas stack where they are admixed with air, ignited and discharged to the atmosphere. In order to control the flow of off-gas from the kiln to the off-gas stack, a damper is provided between the dust settling chamber and the stack.
Conventionally, green coke is feed to the calcining kiln by means of a feed pipe having its outlet end within the upper end of the rotating cylinder defining the calcining kiln. At least a portion of the body of the feed pipe passes through the dust settling chamber, and the inlet end of the feed pipe is normally located above the dust settling chamber for receiving fresh green coke as well as dust which is recycled from the bottom of the dust-settling chamber. In order to maintain the feed pipe in proper position in the dust settling chamber, metal rods or cables attached to the superstructure of the dust settling chamber are employed to support the feed pipe. Normally, the temperatures of the gases generated in the kiln of such an apparatus are about 1300.degree. F.
In a recent modification of the foregoing system, it has been proposed to introduce extra air into the kiln and conduct inceration of the off-gases in the kiln itself rather than in the base of the off-gas stack as is conventional. To this end, suitable air-supply means are added to the kiln for supplying the necessary air. With this design, it has been found that all of the heat necessary to conduct the calcination reaction can be derived from the combustion of the off-gases, thereby totally eliminating the need to supply natural gas or other combustion fuel to the kiln, except for start-up operation. However, it has also been found that when incineration of the off-gases occurs in the kiln itself, the reaction temperature in the kiln is raised to 2000.degree. to 2500.degree. F. Unfortunately, most commercially available metal alloys cannot withstand such high temperatures indefinitely especially when subjected to significant tensile stress. Accordingly, it has been found in practice that conventional feed pipes and the support systems therefor bend, warp and generally become non-servicable at these high temperatures.
Accordingly, it is an object of the present invention to provide an improved feeding system, and especially an improved support system for supporting the feed pipe, for use in a coke calcining apparatus which can withstand the high temperatures involved when the off-gas is incinerated in the kiln itself.
In addition, it is a further object of the present invention to provide an improved feeding system of the type described above which is simple in design, inexpensive to construct and simple to operate.